When a contractor has to perform construction, excavation or other types of work on a site, he uses a variety of heavy machinery. Amongst such machinery, some are used for excavation work, other to move loads up and down and from one location to another. These machines are equipped with booms or mobile arms having sometimes a substantial operating range. The mobility and the extent of the displacement of the boom of these machines are important tools for performing the work, but it is also a great danger for the workers and the various obstacles present within the operating range of the machines. Accidents, which are not only materially costly but also cause major injuries to the workers or even loss of lives, often happen. For example, supporting columns are often knocked down by the boom of a crane. When working close to power lines, there is an ever-present danger from the boom to come in contact with the power lines and often cause the death of the operator or other workers on the site. The latter is particularly important due to the increasing number of power lines now found on working sites. In some areas, it is forbidden by law to work within a specific distance from power lines.
Since human error is the main cause of all accidents, various systems have been proposed to detect excessive displacement of the boom of heavy machinery for the purpose of avoiding overloading or striking of obstacles. Applicants of the present application have also disclosed in U.S. Pat. No. 4,236,864 dated Dec. 2, 1980 a "SAFETY CONTROL SYSTEM FOR THE BOOM OF A CRANE". However, the known systems are mostly electro-mechanical in nature and, thus, lack versatility.